I know there are a few versions that resemble the US box but was under misguided assumption the "US" fin box has definitive measures.

Apparently not.

MFC fins (in US style) are supplied generally with a 3mm step on base (upper part when fitted) which corresponds with base of fin box. Custom versions dont need the step ??? (I think) so some MFC fins are supplied stepless. (???) If you remove the step to facilitate fitting in a custom box does this render fin unsuitable for a "standard" US fin box (as fitted to production boards)

Spoke to MFC and they said for past few years fins have been supplied with step unless they are destined for "custom" boxes.In which case they are flat ????

Isn`t it time we had some standardisation ?????

Have an MFC fin with no step; do I really have to start making "fillers" for fin to sit on ???